Angiotensin II induces α3(IV) collagen expression in cultured murine proximal tubular cells

Angiotensin II (ANG II) induces cellular hypertrophy of cultured proximal tubular cells from various species. This hypertrophic response is associated with an increase in synthesis of basement membrane-associated collagen type IV. Previous investigations by our group have shown that ANG II stimulates mRNA and protein expression of the "classic" alpha 1 and alpha 2(IV) chains in cultured murine proximal tubular cells (murine cortical tubules [MCT cells]). Since it is clearer today that kidney basement membranes also contain heterotrimers of novel type IV collagens, the aim of the present study was to evaluate whether ANG II may influence the expression of alpha 3 and alpha 5(IV) collagen chains in MCT cells. A single dose of 10(-8)-10(-6) M ANG II stimulated mRNA expression of alpha 3(IV), but not of alpha 5(IV), in MCT cells cultured in serum-free media. This response was mediated through AT(1)-receptors because losartan, but not an AT(2)-receptor antagonist, abolished the ANG II-induced expression of alpha 3(IV) transcripts. Transient transfection of MCT cells with transforming growth factor-beta(1) (TGF-beta(1)) antisense phosphorothioate-modified oligonucleotides partly abolished the ANG II-induced alpha 3(IV) mRNA expression. Furthermore, Western blots of cellular lysates incubated with polyclonal antibodies generated against the recombinant collagen chains revealed that ANG II stimulated alpha 3(IV) but not alpha 5(IV) protein expression. This stimulation was partly prevented by co-incubation with a neutralizing anti-TGF-beta(1-3) antibody. In summary, our data indicate that ANG II stimulates expression of the alpha 3(IV) collagen chain in cultured MCT cells, due in part to TGF-beta(1) activation.